This invention relates generally to nonwoven fabrics and particularly concerns a multi-layered, nonwoven, melt-blown fabric having one or more internal layers that are hydrophobic and are sandwiched between one or more exterior layers which are hydrophilic.
Products made of paper and other low-cost, disposable nonwoven webs have been used for a number of years to protect objects from liquid contact. Familiar examples of such protective products include disposable table napkins, bibs, and tablecloths. Even though such disposable protective products are absorbent, moisture which impinges on one surface may still strike through those conventional absorbent protective products and come in contact with the object to be protected.
Particularly with respect to a table napkin, if water is spilled onto the napkin, it is desirable that the napkin provide two functions. First, the surface of the napkin should absorb the water so that the water does not readily run off the napkin surface. Second, the napkin should provide a barrier between the top surface on which the water impinges and the bottom surface so that the water cannot readily strike through to wet the object below, such as the clothing of the napkin user.
In addition a table napkin or other protective product should function as a wipe that will absorb both aqueous liquid and oils from a surface without streaking or leaving residue.
The preparation of thermoplastic microfiber webs is well known and described, for exmple, in Went, Industrial and Engineering Chemistry, Vol. 48, No. 8 (1956) pages 1342 through 1346, as well as in U.S. Pat. Nos. 3,978,185 to Buntin, et al. dated Aug. 31, 1976, 3,795,571 to Prentice dated Mar. 5, 1975, and 3,811,957 to Buntin dated May 21, 1974. These processes generally involve forming a low viscosity thermoplastic polymer melt and extruding filaments into converging air streams which draw the filaments to fine diameters on the average of up to about 10 microns and which break up the filaments into discrete fibers which are then collected to form a nonwoven web.
The Thompson U.S. Pat. No. 3,916,447 discloses a table napkin, or other liquid protective web, which has at least one layer of synthetic polymeric thermoplastic microfibers bonded to at least one layer of cellulosic fibers. In Example 3 of the Thompson patent, a two-ply table napkin is disclosed. The two-ply table napkin is formed by laminating cellulosic tissue (Kleenex single-ply facial grade tissue) and a microfiber web. The tissue has a basis weight of 15.77 grams per square meter. The microfiber web has a basis weight of 15.42 grams per square meter and is formed of melt-blown, naturally hydrophobic, polypropylene fibers having an average fiber diameter in the range of 2 microns to about 6 microns. In Example 5, a disposable handkerchief is disclosed with a tissue laminated to each side of a melt-blown polypropylene web. The tissue layers each have basis weights of 15.77 grams per square meter and the melt-blown web has a basis weight of 7.42 grams per square meter. Consequently, the resulting laminate with the hydrophobic melt-blown polypropylene web is said to have good aqueous liquid barrier properties so that aqueous liquids will not readily strike through the web to the object to be protected.
The Wahlquist et al. U.S. Pat. No. 4,379,192 discloses an absorbent barrier web which is comprised of laminates of fibrous webs and polymeric films. The laminate includes an outer layer of continuous filament spun-bonded material for surface absorption with an inner layer of melt-blown polyolefin microfibers and a backing layer of polymeric film to prevent strike-through. It is suggested that the absorbent capacity of the microfiber polyolefin inner layer may be increased by treating the microfiber mats with a surfactant which may either be sprayed on the microfibers before formation or applied to the surface of the microfiber layer if less absorbent capacity is desired.
The Kitson et al. U.S. Pat. No. 4,196,245 discloses a surgical gown having two internal hydrophobic layers to minimize strike-through. The internal layers are disclosed to be composed of melt-blown polypropylene microfibers. The external layer of the gown may be hydrophobic or hydrophilic and in one embodiment may constitute a spun-bonded rayon web having a basis weight of about 34 grams per square meter which is naturally hydrophilic or which may be treated to be hydrophobic to make the gown liquid repellent.